HDU4004 The Frog's Games（二分）

The Frog's Games

Description
The annual Games in frogs' kingdom started again. The most famous game is the Ironfrog Triathlon. One test in the
Ironfrog Triathlon is jumping. This project requires the frog athletes to jump over the river. The width of the
river is L (1<= L <= 1000000000). There are n (0<= n <= 500000) stones lined up in a straight line from one side
to the other side of the river. The frogs can only jump through the river, but they can land on the stones. If they
fall into the river, they
are out. The frogs was asked to jump at most m (1<= m <= n+1) times. Now the frogs want to know if they want to jump
across the river, at least what ability should they have. (That is the frog's longest jump distance).

Input
The input contains several cases. The first line of each case contains three positive integer L, n, and m.
Then n lines follow. Each stands for the distance from the starting banks to the nth stone, two stone appear in one
place is impossible

Output
For each case, output a integer standing for the frog's ability at least they should have.

Sample Input

6 1 2
2
25 3 3
11
2
18

Sample Output

4
11

 
解决代码：

#include<cstdio>
#include<algorithm>
using namespace std;
const int M = 5*1e5+10;
int a[M];
int L,n,m;
int judge(int x)
{
int cnt=0;
int last=0;
for(int i=1;i<=n+1;)
{
if(a[i]<=last+x){
i++;
}
else
{
if(last==a[i-1])
return false;
last=a[i-1];
cnt++;
}
}
cnt++;
return cnt<=m;

}
int main()
{
while(scanf("%d%d%d",&L,&n,&m)!=EOF)
{
for(int i=1;i<=n;i++)
{
scanf("%d",&a[i]);
}
sort(a+1,a+1+n);
a[n+1]=L;
int l=1,r=L;
int ans;
while(r>=l)
{
int mid=(l+r)/2;
if(judge(mid))
{
ans=mid;
r=mid-1;
}
else
{
l=mid+1;
}
}
printf("%d\n",ans);
}
return 0;
}

<span style="font-size:18px;"><strong>
</strong></span>